Etude du mécanisme et de la cinétique de formation de la phase intermédiaire B dans les alliages du système Al-Mg

Abstract

The aim of the work that we have carried out in this thesis is the study of the kinetics and the mechanism of the formation and the transformation of the intermediate semi coherent phase p’ in the alloys of the Al-Mg system. For this we have used many alloys of the Al-Mg system (8, 9, 10 and 12 wt %t Mg) and several experimental methods simple but rigorous and adapted for this type of scientific works, in order to follow the different structural evolutions : essentially dilatometry and differential scanning calorimetry, completed by optical microscopy, X ray diffraction and micro hardness measurements. The synthesis and the analysis of the numerous and interesting results obtained by those several methods have allowed us to assert that the intermediate p' phase firstly precipitates under the form of globules which cluster then transform to needles leading to a structure identical to a Widmanstatten one, before to come back to the globular form characteristic of the equilibrium p phase. In addition the dilatometry and the differential calorimetrical analysis by a lower degree are sensitive to the structural transformations which occur during the anisothermal heating in all alloys aged at 150°C to precipitate the semi coherent intermediate p’ phase.